Metallkomplexe als Katalysatoren für selektive Olefinoligomerisierungen

Abstract

Due to the importance of alpha-olefin oligomers as intermediates and polymer building blocks for the chemical industry, new single-site catalysts systems that are more active and more selective are constantly being sought. Inserted in this context, we investigated the syntheses of novel organic ligands and the respective metal complexes, to be applied for ethylene and propylene oligomerisation. A group of tridentate imino-ligands was synthesised, which includes the 2,6-bis(imino)pyridines 1-2, the 2,6-diacetyl-monoiminopyridine 3, the iminophosphines 16, and the imidazo[1,5-a]pyridines 23c and 24a, and others, obtaining a range of different N,N,N- or N,N,O- or N,N,P-ligands through variation of the coordinating backbone and of the substituents. The corresponding iron(II) complexes were then prepared and tested for the ethylene oligomerisation in the presence of MAO as co-catalyst. The 2,6-bis(imino)pyridyl-, the 2,6-diacetyl-monoiminopyridyl-, and the iminophosphine iron(II) complexes 5-7, 17 were active catalysts and gave only linear olefins. Furthermore, different classes of bidentate ligands for nickel(II) complexes were synthesised, which are easily tuneable in their steric and electronic properties; for instance the imidazo[1,5-a]pyridines 23a-b and 24b-f, the 3-aminoacrylates 28, 29, and 31, the 3-aminoiminoacrylates 35 and 37. In particular, the syntheses of the differently substituted 3-aminoiminoacrylates required to be developed and optimised according to the different substituents at the acrylic backbone and at the aryl rings. The bidentate N,N-ligands 23a, 24b-d, 40, and 42 were used in their neutral form to yield the corresponding nickel(II) dibromide complexes. The rest of the ligands was deprotonated with sodium bis(trimethylsilyl)amide to yield their monoanionic form that next reacted with [(PPh3)2Ni(Mes)Br]. Two different classes of neutral nickel(II) complexes were obtained: in one class (45 and 46) the ligands actually coordinate as monodentate through their CN-group, while in the latter class of complexes (47-50 and 53) the ligands coordinate as bidentate chelate to the nickel centre. The nickel complexes tested for ethylene oligomerisation gave the best results in the presence of MAO as co-catalyst. Due to the chain-running at the nickel centre, not only linear olefins were formed, but also branched isomers. The propylene dimerisation tests gave the best results with EASC as co-catalyst, and the main products generally consisted of dimers, the fraction C6 always being about 90%. Among the dimers, methylpentenes were the main products in most cases, followed by linear hexenes and small amounts of dimethylbutenes.